jonpjon@ibm.net on thu 14 mar 96
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>I just got a batch of whole round shelves instead of halves. I know the
>rap about 3 vs 4 points. But 3 points just doesn't seem like very much
>with these 21" rounds. Is it adequate? Preferable?
>TIA
>Eleanora
Hi Eleanora,
I`m no ceramic engineer but i still think I`d stick to the 3 points.
I see what you mean though,21" diameter rounds, thats a BIG shelf.
I figure that the distance between posts would be what? about 20" or so.
Four posts might seem better since the distance or span should be
shorter,that would be hmmmm 2pi r divided by.......*&^&^%$%#@ maybe
what? 14" or so,but if one corner doesn`t touch as is apt to happen
like a card table,the span would be much greater. If you used
soft clay wads,about 1/3 of an inch or so,well grogged (I`ve never seen
wads explode but it could be possible,allow some time,say overnight, to
dry or fire slow) you could get the 4 posts to level.
The bigger concern with very large shelves might be stress on the posts
especially if your`re firing high. The weight distribution on 4 posts
,assuming they`re all touching would be much better than on 3. I think
if you took care to use large diameter posts 3 is OK. I`ve been using
cut firebrick to 3 post my 13"by19" 1"thick silicon carbide shelves
which are almost 14yrs old (all cracked and slightly warped but still
good after 300 ^10r firings.)
Don`t hurt your back lifting those things!
Jon Pettyjohn Manila,where we are at the height of one of our only
2 seasons, DRY.
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